1. Field of the Invention
The invention relates to the field of catheters and similar devices used for introducing materials into or removing materials from the bodies of humans and animals.
2. Description of Related Art
Hypodermic needles and lancets have not changed substantially over the past 100 years. For the most part, they are constructed as a hollow, metal, needle-like structure with a bevelled tip, and as such they are quite dangerous. Such needles are involved in the transmission of diseases through "needle sticks" of health care workers, and can break during use, requiring surgical removal.
Needle stick injuries account for approximately 80% of all accidental exposures to blood by health care workers. About 20% of the injuries occur before or during the use of needles, up to 70% occur after use and before disposal(mostly in association with recapping) and the remainder occur during or after disposal.
During the past few years, many new devices intended to reduce the chance of percutaneous injuries have been evaluated. However, the results have been disappointing, and it is not clear that any of the devices have reduced injury rates or have been acceptable to users. Some of the devices have introduced new problems.
Moreover, metal needles, lancets and guidewires are difficult to destroy since they cannot be burned by ordinary means and pose a continuing disposal and health problem. They must be disposed of in separate "sharps" containers and due to the disposal problems have occasionally been disposed of by illegal dumping.
In the past, needle guards have been proposed to reduce the danger of metal hypodermic needles. However, these needle guards have proven to be unwieldy, too costly and inconvenient to use, and injuries have resulted from positioning such needles guards after use of the needles.
Several proposals have been made recently to reduce the hazards associated with metal needles. U.S. Pat. No. 4,976,704 discloses a hypodermic needle made primarily from a metal alloy that loses its rigidity upon exposure to moisture, so that it becomes incapable of repenetrating the skin. The only material disclosed for this use is a particular proprietary machinable aluminum alloy.
U.S. Pat. No. 4,838,877 discloses an injection device constructed of a polymeric material, and U.S. Pat. No. 5,458,614 discloses a needle or a lancet made from a flexible polymeric material which will not pierce the skin by itself, but which is stiffened and made to more readily pierce the skin by working in conjunction with an augmenting structure.
In the field of catheters, it has been proposed to utilize a polymer material which softens at body temperature and/or upon exposure to moisture. Such catheters are disclosed, for example, in U.S. Pat. Nos. 4,846,812 and 5,441,489, and comprise a rigid portion for manipulation of the catheter and a portion which becomes flexible after insertion into the body. This flexibility can be delayed for a period of time to enable the catheter to be properly positioned.
However, when puncturing of the skin is necessary, it is still necessary to make an incision or to puncture the skin with a separate lancet. For example, U.S. Pat. Nos. 4,883,699 and 4,911,691 disclose a catheter formed of a polymer which softens upon absorbing water used in combination with a metal lancet which passes therethrough for puncturing the skin. U.S. Pat. No. 4,955,863 similarly discloses a catheter assembly including a cannula, a needle and a catheter inserter in slidable relationship to the cannula. These devices present the disadvantage that metal lancets are necessary, presenting the safety and disposal problems discussed above. Further, the lancet or guidewire used in connection with the catheter is necessarily longer than the catheter itself, and enters the body first, at which time the practitioner must push the lancet or guidewire further in order to correctly position the catheter. This procedure is a risk to the patient, as the lancet or guidewire may puncture a vessel, membrane, tendon, bone, nerve, lung or spinal cord. Early detection of the appropriate placement of the catheter is not possible with these devices combining a metal lancet or guidewire with a catheter.